Manufacture of tubular articles



March 12, 1963 H. R. JU.RY 3,080,650

MANUFACTURE OF TUBULAR ARTICLES Filed July 3Q, 1959 United States Patent 3,080,650 MANUFACTURE 'F TUBULAR ARTICLES Harold R. Jury, Rose Park, South Australia, Australia,

assignor, by mesne assignments, to Metal Research and Development Limited, Norwood, South Australia,

Australia Filed July 30, 1959, Ser. No. 830,523 4 Claims. (Cl. 29-534) This invention relates to improvements in the manufacture of tubular articles, and in particular it relates to certain improvements in the process of extruding tubular articles from billets of hot metal.

Extrusion of tubular articles is of course well known and this method forms the basis of the present methods of manufacture of many tubular articles. ()ne of the problems which is met in the present methods of manufacture incorporating the extrusion process is the very large amount of force required to extrude the billets to the tubular forms required. It is known that the extent of the deformation which is entailed in an extrusion operation is one of the decisive factors regarding the force which is necessary to apply. It is common practice to give the deformation in terms of the percentage reduction based on the cross sectional areas of the billet before extrusion and after extrusion. a reduction in extrusion percentage, and is calculated by the difference in cross sectional areas divided by the cross sectional area of the billet, the fraction so formed being expressed as a percentage. It is known also that a graphical representation of the extrusion pressure required against the reduction by extrusion expressed in percentage is somewhat of a logarithmic shape, and that as the reduction increases, the extrusion pressure increases very rapidly, the knee of the curve usually lying between ninety and ninety five percent. reduction in extrusion. Thus, under some conditions, a sixty-five percent reduction in extrusion for lead will require about two point five tons per square inch whereas a ninety-five percent reduction under similar conditions requires about seven point five tons per square inch. The effect of these characteristics is to necessitate the use of very heavy machinery for extruding tubular articles when the percentage reduction is high and in the usual methods of extrusion this reduction exceeds ninety-five percent.

It is one of the objects of this invention to provide a means whereby the reduction in extrusion is reduced.

In the production of the ordinary type tubes by the extrusion process it has generally been considered that the essential arrangement requires that a mandrel be passed axially through the billet, and should be located with its tip lying in the aperture of the die so as to form an annular space through which, when pressure is brought to bear on the hot billet by the extrusion ram, the metal is forced out in the form of the tube, the wall thickness of which depends on the ditierence of the diameter of the die aperture and the mandrel. With this usual existing type of arrangement the length of the tube is not governed by the length of the mandrel, but the ram and mandrel move together, the ram acting as a piston inside the container which contains the billet to force the hot metal through the aperture. This type of extrusion is known as direct extrusion. it is known with direct extrusion that the displacement of the billet through the container may take place either by overcoming the interfacial friction between the billet and the container or, where the roughness of the container and the coefficient of friction between the metals tend to control the facility of translation, the displacement of the billet through the container may take place by shearing the hot metal. It is to be noted that the force required to displace the billet in the container with direct extrusion is of the same This is given as.

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order as the force required to shear the outer skin of the billet.

It is therefore an object of this invention to provide a means whereby indirect extrusion may be used in the production of tubular articles so that displacement of the billet in the container at any instant is displacement of extruded metal, and since this is in the form of a tubular article, the frictional resistance to displacement is very much reduced.

1 Both the above mentioned objects have been achieved to some degree in the production of certain types of tubes, such as for example collapsible tooth paste tubes. In the productionof collapsible tubes the usual method of production is for a slug of metal, being disc like in shape, to be placed in a conical based die, and for a punch to enter the die, the diameter of the punch being slightly less than the diameter of the die, so that the metal is extruded in tubular form up over the punch as it enters down into the die. The punch is then removed from the die, carrying the collapsible tube with it, and the collapsible tube is stripped from the punch, this operation being comparatively easy because of the nature of the tube which has been formed, that is the tube is very thin and is made from a flexible metal or other material, and may readily expand sufficiently to be stripped from the punch. This method, however, is not generally used '2 for theproduction of tubes of substantial thickness for the reason that the tubes being formed of hot metal tend to'shrink over the die and are not readily removed therefrom.

It is a further object of this invention to provide a means whereby tubular articles may be extruded over a punch or mandrel and removed therefrom after extrusion.

When the tubes are extruded from billets it has previously been thought necessary or preferable to use a billet with a central hole. This then increases the requiredouter diameter of the billet and thus also increases its cross sectional area for a given rate of cooling, due to the additional cooling effect of a mandrel.

it is therefore a further object of this invention to provide means whereby a solid billet may be used.

According to this invention, a method of manufacturing tubular articles comprises heating a billet of metal, indirectly extruding the billet over a mandrel with an enlarged removable end, shearing the closed end of the article which has been formed by extrusion, removing the enlarged end from the mandrel, and removing the tubular article from the mandrel.

For the invention to be more clearly understood, an embodiment will be described with reference to the ac companying drawings, in which FIG. 1 is a diagrammatic elevation of a press, showing extrusion dies in position,

FIG. 2 is a sectional elevation, showing a billet partly extruded over the mandrel,

FIG. 3 is a partly sectioned elevation showing the billet fully extruded, and a ring die in position for shearing the cap from the billet, and

FIG. 4 shows the position of the tools after shearing the cap.

The description is limited to the production of a four inch tube, but of course it will be realised that the invention is not so limited and may be used for tubes over a very large range of sizes.

Referring first to FIG. 1, an extrusion press 1 has a moving platen 2 and a fixed platen 3 arranged in the normal way. The extrusion tool comprises a container 4 0n the moving platen 2, and a mandrel 5 on the fixedplaten 3.

The container 4 is made about four inches in diameter and approximately the same length as the billet which is 3 to be used. The billet 6 which is to be used is made solid and has no hole as is usual in the manufacture of tubes, this feature enabling the billet 6 to retain its heat, whereas if a hole were pierced of say one inch in diameter, as is usual in the manufacture of tubes of about four inch diameter, then it would be found desirable for the overall diameter of the billet to be about six or seven inches. By this means it will be seen that the percentage reduction may be considerably reduced, and therefore the amount of actual force required to extrude the tube will be reduced also, but to a very much greater extent, because of the above described somewhat logarithmic relationship between the reduction in extrusion percentage and the extrusion pressure.

The billet is then located over the mandrel S which is co-axial with the container 4, the length of the mandrel being within the limits that its ratio will withstand the pressure to be applied to the mandrel 5 without any undue displacement of the upper end of the mandrel, but the length of the mandrel 5 is at least four times its diameter, so that its upper end can deflect sufficiently to centralize itself under conditions of metal flow and thereby accommodate the tolerances existing in the press. The mandrel 5 itself is made in two portions, the main part 7 extending upwardly being of slightly less diameter than the inner diameter of the tubular article 8 which is to be formed, and the main part 7 has a concentrically held removable end 9, which is of enlarged diameter compared with the main part 7. This enlarged removable end 9 has a substantially shallow ridge 10, the diameter of which determines the inner diameter of the tubular article 8, and a domed upper surface 11 to facilitate flow of the plastic metal during extrusion.

The container 4 is moved relatively to the mandrel 5, or vice versa, and extrusion takes place in the annular space between the ridge of the mandrel 5 and the inner diameter of the container 4, the tubular article 8 being formed over the mandrel 5.

After the tubular article 8 has been extruded the container 4 is moved away from the mandrel 5, and a ring die 13 is located over the closed end 14 of the tubular article 8 (see FIG. 3), and the press 1 is used to force the ring die 13 over the shallow ridge 10 of the removable end 9 of the mandrel 5, to shear the closed end 14 from the tubular article 8, the end 14 being left in the space between the removable end 9 of the mandrel 5 and the end face of the container 4.

After the tubular article 8 has thus forced off the shallow ridge 10 of the mandrel 5 it will be loosely engaged on the main part 7 of the mandrel, and when the removable end 9 of the mandrel 5 is removed it will be seen that the tubular article 8 may be readily removed.

It will be seen that by this method the length of tubes which may be produced in a single extrusion operation are comparatively short, but it is known to be a cheap operation to draw such a tube out to a longer length smaller diameter thinner wall tube on a draw bench, and since the size of the press required to extrude the tube is very much smaller than in the usual existing process for production of extruded tube (in this instance the pressures required were found to be ninety-six tons compared with more than one thousand tons in the orthodox process), it will be clearly understood that the cost of production of tubes will be very much less than by the usual existing method.

It will be seen that this method may be used for the production of tubes not merely from the so-called soft metals, but from any other metal which may be extruded, and it will also be appreciated that because of the great reduction in the percentage of extrusion, that is the comparison of the cross sectional area of the billet with the cross sectional area of the metal in the tube, then much smaller presses may be used for production of these tubes.

It will also be appreciated that a further saving is effected by the elimination of the central hole in the billet.

According to a second embodiment which is not illustrated, greater length tubes may be produced by using a longer mandrel supported at its fixed end in such a way that the free end of the mandrel is able to move in two vertical planes. Use is again made of the tendency for a mandrel which is central with the die aperture to remain central as the metal commences to flow.

Since the ratio of the mandrel, that is, the slenderness ratio, Where l is the length of the column and r is the least radius of gyration, may exceed permissible limits, that is, the mandrel may tend to buckle, it may be found necessary to fit fixed formed rollers around the mandrel at or near its central point. These rollers are arranged to contact the mandrel, or stand away from the mandrel by a distance equal to the tube wall thickness, so they would prevent the mandrel from buckling at all when the tube passes between them, or would limit the buckling before that time to be not more than the tube wall thickness, this being considered negligible.

The upper free end of the mandrel may be centralised by some removable means, say a segmented annular tapered wall ring which is expanded outwardly by the container or by the extruded tube.

Of course it will be seen that many further variations could be introduced, such as means to hold the mandrel concentric with the container, these means involving the use of guide pins and bushes or other known devices, or the method of forcing the tube over the removable portion of the mandrel, which could be varied in any known manner.

While the illustration in FIG. 1 shows the mandrel 5 fixed in relation to the fixed platen 3, it will be appreciated that, if the tubular article 8 exceeds a certain length for a press of a given stroke, the mandrel 5 may need to be moved out of alignment with the container 4, for the purposes of removing the tubular article 8 from the mandrel 5, but it will be noted that for many operations this feature need not be included, since the main part 7 of the mandrel 5 is of smaller diameter than the tubular article 8, and therefore the tubular article 8 can be removed non co-axially from the mandrel, thus avoiding the container during removal.

What I claim is:

l. The method of extruding tubular articles from extrusile metal, consisting of the steps of heating a billet of extrusile metal to a temperature suitable for extrusion, placing said heated billet in an inverted closed end container, urging said closed end container downwardly over a removable enlarged end of a fixed upstanding mandrel the length of which exceeds four times its diameter, said mandrel disposed coaxially to said container, so as to form a parallel sided tubular article with a closed end, retracting said container from said tubular article, shearing said closed end from said tubular article and at the same time urging the tubular article downwardly over said enlarged end, removing said enlarged end from said mandrel, whereby the sides of said tubular article are solely and loosely engaged by said fixed upstanding mandrel, and removing said tubular article from said mandrel.

2. The method of extruding tubular articles from extrusile metal, consisting of the steps of heating a billet of extrusile metal to a temperature suitable for extrusion, placing said heated billet in an inverted closed end container, urging upwardly into said closed end container a removable enlarged end of a fixed upstanding mandrel the length of which exceeds four times its diameter, said mandrel disposed coaxially to said container, so as to form a parallel sided tubular article with a closed end, retracting said tubular article on said mandrel from said container, shearing said closed end from said tubular article and at the same time urging the tubular article downwardly over said enlarged end, removing said enlarged end from said mandrel, whereby the sides of said tubular article are solely and loosely engaged by said fixed upstanding mandrel, and removing said tubular article from said mandrel.

3. In the extruding of tubular articles from extrus-ile metal, the method consisting of the steps of heating a billet of extrusile metal to a temperature suitable for extrusion, placing said heated billet in an inverted closed end container, extruding said billet downwardly over a removable enlarged end of a fixed upstanding mandrel the length of which exceeds four times its diameter so as to form a parallel sided tubular article with a closed end, retracting said container from said tubular article, urging a ring die over the closed end of the tubular article to shear the closed end from said tubular article and at the same time urging the tubular article downwardly over said enlarged end, removing said enlarged end from said mandrel by hand, whereby the sides of said tubular article are solely and loosely engaged by said fixed upstanding mandrel, and removing said tubular article from said mandrel by hand.

4. In the extruding of tubular articles from extrusile metal using an extrusion press, an inverted closed end container on the moving platen of said press, a fixed upstanding mandrel on the fixed platen of said press coaxial with said container, the length of the mandrel exceeding four times its diameter, a removable enlarged end to fit the end of said mandrel and a ring die positionable by hand, the method consisting of the steps of placing said enlarged end on said mandrel, heating a billet of extrusile metal to a temperature suitable for extrusion, placing said heated billet in said inverted closed end container, operating the extrusion press to extrude said billet downwardly over the removable enlarged end of said mandrel so as to form a parallel sided tubular article with a closed end, retracting said container from said tubular article, hand positioning said ring die over the closed end of the tubular article, operating the press to shear the closed end from said tubular article and at the same time urging the tubular article downwardly over said enlarged end, removing said enlarged end from said mandrel by hand, whereby the sides of said tubular article are solely and loosely engaged by said fixed upstanding mandrel, and removing said tubular article from said mandrel by hand.

References Cited in the file of this patent UNITED STATES PATENTS 2,483,376 Temple Sept. 27, 1949 2,679,931 Cigliano June 1, 1954 2,804,790 Lefere Sept. 3, 1957 2,812,059 Biginelli Nov. 5, 1957 

1. THE METHOD OF EXTRUDING TUBULAR ARTICLES FROM EXTRUSILE METAL, CONSISTING OF THE STEPS OF HEATING A BILLET OF EXTRUSILE METAL TO A TEMPERATURE SUITABLE FOR EXTRUSION, PLACING SAID HEATED BILLET IN AN INVERTED CLOSED END CONTAINER, URGING SAID CLOSED END CONTAINER DOWNWARDLY OVER A REMOVABLE ENLARGED END OF A FIXED UPSTANDING MANDREL THE LENGTH OF WHICH EXCEEDS FOUR TIMES ITS DIAMETER, SAID MANDREL DISPOSED COAXIALLY TO SAID CONTAINER, SO AS TO FORM A PARALLEL SIDED TUBULAR ARTICLE WITH A CLOSED END, RETRACTING SAID CONTAINER FROM SAID TUBULAR ARTICLE, SHEARING SAID CLOSED END FROM SAID TUBULAR ARTICLE AND AT THE SAME TIME 